With a rapid increase in the use of fossil fuels, there is an increasing demand for use of alternative energy or clean energy. The field of electricity generation and accumulation using an electrochemical reaction has been most actively studied to meet the increasing demand.
As a representative example of electrochemical devices using such electrochemical energy, secondary batteries are currently used and an application area thereof has gradually been increased. Recently, with an increase in development of technology and demand for portable devices, such as portable computers, mobile phones, cameras, and the like, demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, much research on lithium secondary batteries, which have high energy density, high operating voltage, a long cycle lifespan, and a low self-discharge rate, has been conducted, and such lithium secondary batteries are commercially available and widely used.
Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. In the secondary battery, lithium ions emitted from a positive electrode active material are intercalated into a negative electrode active material such as a carbon particle through 1st charging and the lithium ions are deintercalated through discharging. As lithium ions reciprocate between opposite electrodes as such, they transfer energy. Therefore, the secondary battery can be charged and discharged.
An amount of an active material in a positive electrode is the most important factor that determines charge and discharge capacity of a battery. Therefore, in order to manufacture a high-capacity electrode, a high level of a positive electrode active material is loaded on a surface of a current collector. However, in the case of a positive electrode in which a high level of an active material is loaded, electrolyte wetting with respect to an active material layer is reduced, and charging and discharging characteristics, such as quick charging and output characteristics, of a battery are degraded due to a difference in reactivity in a thickness direction of an electrode.
In order to solve the problem, a method of increasing the porosity of an active material layer has been used, but when an active material layer having high porosity is used to realize the same level of capacity, a thickness of an electrode becomes thick. Accordingly, a problem in designing a cell having high energy density arises.
Therefore, there is a need to develop a positive electrode which may improve electrolyte wetting and enhance charging and discharging characteristics of a battery while maintaining high capacity of the battery.